The recently published 1997 Uniform Building Code incorporates two significant changes to the ground shaking
criteria which apply to all structures. The first change is a revision to soil types and soil amplification factors.
The second change is the incorporation of near source factors in UBC seismic Zone 4. Together these changes result
in the largest increases in code ground shaking criteria which has occurred in the past 30 years. Records obtained
from the strong motion Instrumentation Program (SMIP) along with USGS records were the primary sources of data used
to justify these code changes.